Method of preserving fruits



Patented Oct. 25, 1938 Ralph E. Schaefle, Berkeley,

calla, assignor to r,

Balfour, Guthrie & .00., Limited, San Francisco, Calii'., a corporatlon of Delaware I No Drawing. Application May 11,1938,

. Serial No. 201,3 9 a Thlsinvention relates to a method for preserving fruits, .especiallyprunes and like dried products, the main purpose of the invention being to providea method which lends itself to practice on a commercial scale and which results in a preservation enhancing of the natural taste, appearance and-quality of the product treated. vr

Bythe ordinary method of preparing prunes for the.table,gthe prunes are cooked, i. e. boiled,

10 in water to cause the prunes toswell and soften.

This results in a diffusion of the water into the bodies'of the prunes, and at a very rapid rate, causing the. prunes to swell and often-burst. Furthermore, it leaches out the sugar and" destroys muchof the original prune flavor, and results in actual deterioration of the prunes.

Actual tests show that a dried commercial prune contains about sugar and about the same amount 01' moisture. The completed prod- 20 uct obtained by the method of preserving here described contains about 46% moisture, and the sugar content is maintained at about the same ratio.

In accordance with the present invention, one 5 object is the preservation of the prune by the incorporation of sugar in substantially the same proportion as that found in the original dried prune, so as to retain as unaltered as possible the original and characteristic sweet, prune flavor. While moisture is at the same time introduced,

the prunes are not cooked or boiled but are sub- Jected to a sufliciently high and regulated tem- I perature for an adequate period of time to insure a skin and pulp of desired tenderness. Thereafter the prunes are drained of excess syrup and made ready for the market.

More specifically, by this new process, the

dried prunes are first processed by dipping them in hot water for about four minutes. This is merely a cleansing operation and effects littleif any change in the physical structure of the prune itself.

The prunes are next removed and drained, and

while hot are placed in a kettle containing a syrupy solution made from sugar and water,

about half and half by weight, so as to produce a solution of about Baum. The kettle may be heated in any suitable manner, for instance by a steam jacket, and the temperature is so controlled 5 as not to cook or boil the prunes. The syrup and the prunes placed therein are maintained in practice at a temperature of approximately 200 F. for about two hours. The steam is then turned 01! and the prunes are left in the syrup solution 5 (or an additional sixteen hours, approximately,

during which time thetemperature is allowed gradually to drop to approximately 160 F. *The prunes are then removed-and drained and are packed in cans, glass jarsorother suitable containers, after which the containers are evacuated, 5 sealedand finally subjected to a sterilizing temperatureand thereafter cooled, when they are ready for the market. t j' Prunes preserved by themethod herein de scribeddistinguish outstandingly from ordinary 1| cooked or stewed prunes by being more tender, by having a better appearance, and-by retaining their original flavor and sweetness and byv being more palatable. The prunes are at notime subjected to aboiling temperature. Their heat treat- 15 ment in the syrup solution at amaximum temperature of 200 F. and then graduated down to 160 for a considerable period of time brings about a structural change without depriving the, prunes of any of their inherent virtues. While 1 the prunes are tender and the flesh or meat is readily separated from the pits, they are at the same time sufliciently firm to prevent breaking up or becoming mushy during shipment.

On account of being subjected to a temperature 25 below the boiling point of water, the prunes do not have the burnt caramel or bitter taste that many prunes have which are cooked in water, such as canned or stewed prunes. The ordinary cooking or stewing process is really a leaching my process, while the present method is designed to have the opposite effect in that it takes nothing fromthe prunes, as the long treatment andthe .low temperature employed causes the prunes to retain all their mineral salts and fruit sugar. 5

In the present product, due to the comparatively low temperature maintained and the length of time employed, the sugar solution enters the prune slowly, and as the sugar or syrup solution is approximately the same as the sugar solution in the inside of the prune, no leaching efiect can take place. Again, due to'the comparatively low temperature and length of time required, diffusion takes place slowly, and the danger of bursting the prune is entirely obviated. The long period of 45 treatment also insures tenderness of the skin and pulp of the prune, and ready separation from the pit takes place when'it is finally eaten.

One measure of distinction between prunes treated by this process and so-called candied" 50 prunes or stewed prunes is by what is known as the penetration test.

Penetration test Thisis a test to determinethe relative penetra- .2 J am o 10 mately 25% moisture content, may require a force 0! up to 290 grams. The ordinary stewed or canned prunes, with a moisture content 01- ap proximately 72%, will yield to'penetration under a load of from 6 to 22 grams. 1s A so-called "candied" prune, with n -moisture content of apprqximately 351% would require loading from 50 to 94 grams before the needle will penetrate the prune. On the other hand, prunes treated and preserved according to the Ii present method will possess a moisture content of approximately 46% and will require a load for penetration of from only 10 to 25 grams.

The conclusions drawn from the foregoing comparisons show as a matter of fact that, although ii the penetration tests for ordinary stewed prunes andior the present process appear to overlap each other, the present method, while resulting in a skin equal in penetrability to that of the stewed prune, has the marked advantage of insuring an 10 unbroken skin as against the burst skin of a stewed prune. Besides, the present method produces a product of greatly reduced-moisture content compared with the stewed prune, with'a much. higher sugar content. a 86 i In short, prunes preserved bythe present methsolution at oddistinguish not only in appearance, tenderness and flavor over previous methods at treating pnmes, but also in firmness, moisture and sugar content. 7

While the specification describes the preserving I of prunes, it should be understood that the is equally applicable to other dried fruits. Having thus described my invention, what I claim and desire to secure byiettera Patent isl. A method of preserving dried prunes which 10 consists in submergins the prunes in a sugar so- :lution of substantially the same sugar content as that or the dried prunes, maintaining the sugar a temperature of approximately 7 1'". for a predetermined period, retaining the i6 prunes in the sugar solution until the flesh and skin has become suiiicientiy tender to separate "from the pit readily and at the same time permitting the sugar solution to cool gradually. removing the prunes from the sugar solution, and D then vacuum-packing and sterilizing the prunes.

.2. A method'ot preservingdried prunes which consists in submerging the prunes in a sugar solution 0! substantially the same sugar content as that or the dried prunes, maintaining the sugar as solution and the prunes submerged therein at a temperature or approximately 300' l". for a period of about two hours, retaining the prunes inthe sugar solution for an additional period 0! about sixteen hoursand at the same time gradually cooling the prunes and sugar solution to a temperature of approximately 160' It. removing the prunes from the sugar solution, and then vacuumpacking and sterilizing the prunes.-

, a i RALPH 2. 56mm 8 

